Nonaqueous electrolyte solution lithium ion batteries or lithium secondary batteries comprising a carbon material, an oxide, a lithium alloy or a lithium metal as a negative electrode, and a lithium-containing transition metal complex oxide as a positive electrode, and further comprising an electrolyte solution containing a chain or cyclic carbonate solvent, have attracted attention as power supplies for cellular phones, laptop computers or the like because they can achieve a high energy density. Recently, they have attracted attention also as power supplies for motor drive in hybrid electric vehicles (HEV) or the like because of the improvement of output characteristics and long-term reliability such as a storage characteristic.
In these secondary batteries, it is known that, for purpose of suppressing a reaction between the surface of negative electrodes and the solvent molecule, additives are added to the electrolyte solution to form a film called protective coating (or coating, SEI) derived from the additives on the surface of the negative electrodes utilizing an electrochemical reaction in a charge/discharge process, thereby improving the basic characteristics and reliability of the secondary battery. The coating significantly affects charge/discharge efficiency, cycle lifetime and safety, and therefore it is known that the formation and control of the coating on the surface of negative electrodes is essential in order to achieve a battery with a high performance. Although a secondary battery using a coating-forming additive for an electrolyte solution exhibits very excellent battery characteristics, the secondary battery had problems as follows.
When a coating-forming additive is added to an electrolyte solution, the electrolyte solution contacts not only with a negative electrode, but also with a positive electrode, and therefore a decomposition product of the additive is generated due to oxidation decomposition on the surface of the positive electrode. The decomposition product of the additive is eluted in the electrolyte solution to cause the increase of the viscosity and the reduction of the ion conductivity of the electrolyte solution, which deteriorates the battery characteristics. In addition, also after the formation of a coating in a charge/discharge process, the additive in the electrolyte solution is not completely consumed and a part thereof remains, and therefore repeated charging/discharging grows a new coating to cause the increase of the internal resistance of the negative electrode, which deteriorates the battery characteristics. Further, a coating-forming additive is generally highly reactive, and had a problem of a poor storage stability in an electrolyte solution.
On the other hand, Patent Literature 1 and Patent Literature 2 describe a method for producing an electrode by adding a coating-forming additive in a negative electrode slurry.